Abstract
Satellite remote sensing has transformed our understanding of Earth processes. One component of the Earth system where large uncertainties remain are Arctic and boreal freshwater lakes. With only short periods of open water due to annual ice cover, lake productivity in these regions is extremely sensitive to warming induced changes in ice cover. At the same time, productivity dynamics in these lakes vary enormously, even over short distances, making it difficult to understand these potential changes. A major impediment to an improved understanding of lake dynamics has been sparsely distributed field measurements, in large part due to the complexity and expense of conducting scientific research in remote northern latitudes. This project overcomes that hurdle by using a new set of ‘eyes in the sky’, the Planet Labs CubeSat fleet, to observe 35 lakes across 3 different arctic-boreal ecoregions in western North America. We extract time series of lake reflectance to identify ice-out and green-up across three years (2017–2019). We find that lakes with later ice-out have significantly faster green-ups. Our results also show ice-out varies latitudinally by 38 days from south to north, but only varies across years by ~9 days. In contrast, green-up varied between years by 22 days in addition to showing significant spatial variability. We compare PlanetScope to Sentinel-2 data and independently validate our ice-out estimates, finding an ice-out mean absolute difference (MAD) ~9 days. This study demonstrates the potential of using CubeSat imagery to monitor the timing and magnitude of ice-off and green-up at high spatiotemporal resolution.
Highlights
High northern latitudes are rich in lakes [1,2] and experiencing dramatic warming [3]with global consequences
Over 1037 total PlanetScope scenes were acquired over our study area from 2017–2019, with an average of about 18–20 scenes per week per lake
We found differ2019 average mean absolute difference between PlanetScope and Sentinel-2 was ences were greater during the ice-free period thanallduring ice-covered period
Summary
High northern latitudes are rich in lakes [1,2] and experiencing dramatic warming [3]with global consequences. Arctic and boreal lakes are experiencing changes in the timing of ice-out [4,5,6] and primary productivity [7]. A recent study has shown that ice-out globally has advanced 8 days over the past 100 years [8] and 13 days since 2000 in parts of the Arctic [9]. Air temperature has been shown to be the primary control on ice-out timing [10,11] with ice-out varying along latitudinal climate gradients. Because loss of ice cover can accelerate temperature-driven changes in water transparency, heat budgets and mixing regimes [13], climate change may have strong effects on lake productivity
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